CN108599605B - Three-level inverter model prediction Poewr control method based on two Vector modulations - Google Patents
Three-level inverter model prediction Poewr control method based on two Vector modulations Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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Abstract
The invention discloses a kind of three-level inverter model prediction Poewr control method based on two Vector modulations, the instantaneous active and reactive power of gird-connected inverter is adjusted based on the model prediction power control of two Vector modulations, and balance mid-point voltage；Model prediction power control based on two Vector modulations is divided into two steps, establish two cost functions, the small sector where desired voltage vector is first acquired, two vectors are then selected by reasonable cost function and adjusts its duty ratio to control each switching device of three-level inverter.The method of the present invention may be implemented switching frequency and fix, and reduce the operand of algorithm, save computing resource, and the inverter stable state of method control and dynamic property all show well.
Description
Technical field
The present invention relates to three-level inverter control technology field, in particular to a kind of three level based on two Vector modulations
Inverter model prediction power control method.
Background technique
With getting worse for environmental pollution and energy crisis, the distributed hair of the renewable energy such as solar energy, wind energy is utilized
Power technology is by more and more extensive concern.And inverter is the interface of distributed generation system and power grid, with two traditional electricity
Flat inverter is compared, and three-level inverter harmonic content is low, and switching loss is small, and power quality and efficiency will be much higher.
Model Predictive Control is a kind of novel predictive control strategy, which, which needs to establish one, can predict behavior in future
System model, usually construct a cost function, selection makes this cost function reach the optimized switching state of minimum value, just
Predicted value can be made close to target value.Predictive control algorithm about three-level inverter have earliest model prediction power control and
Model prediction current control.These predictive control algorithms can be with the mid-point voltage of balancing three-level inverter, but both are passed
The switching frequency of system method is all variation, all only selects an optimal voltage vector defeated as voltage in a switch periods
Out, without rule, such output has higher requirement to sample frequency and switching frequency is not fixed, humorous for the variation of switch state
Wave frequency spectrum is wide, brings difficulty to the design of output filter.Currently, being used for the prediction optimized switching sequence Direct Power of inverter
Control and modulation pattern predictive control strategy are suggested, and both methods may be implemented fixed switching frequency, but calculation amount compared with
Greatly, and in a switching frequency switch state used has 3, and inverter switching states switching times is caused to increase.
Summary of the invention
The purpose of the present invention is to overcome the shortcomings of the existing technology and deficiency, provides a kind of three electricity based on two Vector modulations
Flat inverter model prediction power control method overcomes existing three-level inverter control strategy switching frequency to change, and calculates
Larger disadvantage is measured, realizes constant switching frequency, reduces switching number, reduces the operand of algorithm, saves computing resource.
The purpose of the present invention is realized by the following technical solution:
A kind of three-level inverter model prediction Poewr control method based on two Vector modulations, comprising: by all 27
A switch state is divided into 12 small sectors on the basis of traditional 6 big sectors；First cost function selection packet of the first step
Then small sector where vector containing desired output voltage passes through in the small sector that second cost function obtains in the first step
Optimal two vector switch sequence is selected, the corresponding switch state of two vectors finally selected using three-level inverter, according to
Corresponding duty ratio controls the device for power switching of inverter.
Specific step is as follows:
It under the influence of negligible resistance, finds out in three phase network at static two phase coordinate systems α β, active power and idle
The differential equation of power:
Wherein, (eα,eβ) and (iα,iβ) network voltage and electric current under static two phase coordinate systems α β are represented, L is exchange filter
The inductance of wave device, ω indicate that electrical angular speed, P represent active power, and Q represents reactive power, when inverter switching states are vi
When, the voltage that inverter is exported at static two phase coordinate systems α β is ui(uαi,uβi), be input to grid side active power with it is idle
The derivative of power is expressed as fpi,fqi, so above formula can also be indicated are as follows:
Assuming that active power and reactive power of the three-level inverter when k-th of sampling period starts are respectively P (k), Q
(k), by two voltage vector voltage vector ui,ujT is acted on respectivelyi,tjAfter time, when+1 sampling period of kth starts,
The active power and reactive power predicted value of inverter output are as follows:
If the sampling time is Ts, since each sampling period, only there are two vectors to act on, so Ts=ti+tj；
Zero vector is taken respectively, and the middle big vector of vector sum forms the center of small sector, utilizes this 12 centrally located vectors
Calculate separately the active-power P (k+1) and reactive power Q (k+1) of+1 start time in sampling period of kth；Define a cost
At this moment function does not consider capacitor midpoint first from the sector found out where making the smallest center vector of cost function in calculated result
The balance of voltage defines cost function J ' are as follows:
J '=[Pref-P(k)-fpcTs]2+[Qref-Q(k)-fqcTs]2 (4)
Wherein, PrefIt is given active power value, QrefIt is given reactive power value, and fpc,fqcIt is output center arrow
The change rate for measuring corresponding active power and reactive power, finding out from above-mentioned calculated result makes the smallest center cost function J '
Sector where vector, then sector where two vectors needed for the sector is；
It, first will be to two vectorial combination each in small sector most in seeking small sector before optimal two vector switch sequence
Excellent duty ratio is calculated, and the action time of two of them vector is respectively tiAnd tj, tiIt can be by enabling cost function J to ti
Derivation, and enable it be equal to 0 and obtain, define cost function J are as follows:
J=Δ P2+ΔQ2=[Pref-P(k)-fpiti-fpjtj]2+[Qref-Q(k)-fqiti-fqjtj]2 (5)
It obtains calculating tiFormula are as follows:
In addition, by Ts=ti+tjObtain tj=Ts-ti；
In cost function, neutral point voltage balance, mid-point voltage equation are considered are as follows:
Wherein, uo=uc2-uc1For the voltage difference of bus capacitor, C is the size of two capacitors of DC side, viabcFor inverter
Switch state, tiIt is the corresponding effect duration of switch state, | viabc|={ | via|,|vib|,|vic|}T,vix(x=a, b, c)
∈ { -1,0,1 }, iabcIt is the line current and i of connected systemabc={ ia,ib,ic}；
Consider capacitor neutral point voltage balance, find out in small sector the optimal two vector switch sequence in a switch periods,
Define cost function J " are as follows:
J "=[Pref-P(k)-fpiti-fpjtj]2+[Qref-Q(k)-fqiti-fqjtj]2+λ|uo(k+1)| (8)
Finding out from above-mentioned calculated result makes cost function be minimized corresponding two vectors, corresponding according on off sequence
Duty ratio, synthesis make the smallest optimal vector of cost function；
Finally, being controlled using two obtained vectors and its corresponding duty ratio three-level inverter.
Specifically, the value of λ is 0.1 in formula (8).
Preferably, in order to avoid being not in the switching between N and P when the switching of adjacent sectors switch state, using small arrow
Implementation method in quantity set exports two vector switch sequences, i.e., small vector is placed among on off sequence, by zero vector/middle arrow
Amount/big vector action time equal part is on both sides.
Compared with the prior art, the invention has the following advantages and beneficial effects:
The present invention is on the basis of Model Predictive Control, using the model prediction power control based on two Vector modulations, phase
Than in traditional three-level inverter Model Predictive Control, realizing constant switching frequency control, two capacitors of active balance
Mid-point voltage, improve the performance of three-level inverter, reduce the harmonic content of output electric current, relative to predicting optimal to open
Sequence direct Power Control and modulation pattern PREDICTIVE CONTROL are closed, reduces switching number, reduces a large amount of operand, is saved
The about computing resource of control chip.
Detailed description of the invention
Fig. 1 is three level grid-connected inverter circuit diagrams.
Fig. 2 is three-level inverter space voltage vector figure.
Fig. 3 is three-level inverter space vector sector figure.
Fig. 4 is the geometric interpretation of the cost function J when desired voltage vector is between two vectors.
The geometric interpretation of cost function J when Fig. 5 is except desired voltage vector is located at two vectors.
Fig. 6 is that desired voltage vector and the geometry of small sector centers vector contact.
Fig. 7 is the three-level inverter model prediction power control system flow chart based on two Vector modulations.
Fig. 8 is the dynamic of inverter output line voltage in the model prediction power control system emulation based on two Vector modulations
Response.
Fig. 9 is the dynamic response of power grid line current in the model prediction power control system emulation based on two Vector modulations.
Figure 10 is electric network active and idle dynamic in the model prediction power control system emulation based on two Vector modulations
Response.
Figure 11 is the dynamic of the DC capacitor voltage of the model prediction power control system emulation based on two Vector modulations
Response.
Specific embodiment
Present invention will now be described in further detail with reference to the embodiments and the accompanying drawings, but embodiments of the present invention are unlimited
In this.
Embodiment 1
In Fig. 1, give three level grid-connected inverter circuit diagrams, three-level three-phase inverter by filter inductance L with
And equivalent resistance R is connected with power grid.
In Fig. 2, the corresponding space voltage vector of 27 switch states is given, each switch state corresponds to sound
The voltage vector for the inverter output answered.
When inverter switching states are viWhen, the voltage vector of three-level inverter output is ui(uαi,uβi), three level are inverse
Become the output voltage vector u of deviceiIt can be acquired by grid line voltage vector e, line current vector i and inductance L and resistance R:
In formula (1), by ignoring the resistance of filter, converted by Clark, it can be static to two-phase by equation transform
Under coordinate system α β:
Wherein, (eα,eβ) and (iα,iβ) represent network voltage and electric current under static two phase coordinate systems α β.
By taking three-phase voltage as an example, Clark transformation for mula is as follows:
Wherein, eαAnd eβBetween have following relationship:
Wherein, E indicates that grid voltage amplitude, ω indicate electrical angular speed.
Instantaneous active power and reactive power can be obtained by following formula at two-phase stationary coordinate system α β:
Wherein, P is represented active, and Q represents idle.It is instantaneous on convolution (2), formula (4) and two-phase stationary coordinate system α β
The formula (5) of active power and reactive power obtains the differential of the active power and reactive power at two-phase stationary coordinate system α β
Equation are as follows:
When inverter switching states are viWhen, the voltage that inverter is exported at static two phase coordinate systems α β is ui(uαi,
uβi), the derivative for being input to grid side active power and reactive power is expressed as fpi, fqi.So above formula can also be indicated
Are as follows:
Active power and reactive power of the three-level inverter when k-th of sampling period starts are respectively P (k), Q (k),
By two voltage vector ui,ujT is acted on respectivelyi,tjAfter time, when+1 sampling period of kth starts, it is active and it is idle can
To be written as:
If the sampling time is Ts, since each sampling period, only there are two vectors to act on, so Ts=ti+tj.Active power
P (k+1) and reactive power Q (k+1) are active and idle predicted values when starting in+1 sampling period of kth.
In conjunction with the cost function of conventional model PREDICTIVE CONTROL, when not considering the influence of mid-point voltage, can be obtained by formula (8)
Cost function J to two vector switch series model PREDICTIVE CONTROLs can be indicated are as follows:
J=Δ P2+ΔQ2=[Pref-P(k)-fpiti-fpjtj]2+[Qref-Q(k)-fqiti-fqjtj]2 (9)
In Fig. 3, region division is carried out to the three-level inverter space voltage vector figure in Fig. 2, to be based on
The model prediction power control of two Vector modulations.Consider the problems of to control neutral point voltage balance to the end, when on off sequence is by two
When a switch state forms, it is necessary to which the on off sequence of the switch state comprising a small vector, each small sector is as shown in table 1.
Wherein null vector includes three switch states (PPP, OOO and NNN), replaces opening for three all null vectors with OOO herein
Off status is left 25 switch states.For traditional optimizing strategy, need to carry out 48 calculating cycles to acquire most
Excellent two vector, and the optimizing strategy of the model prediction power control based on two Vector modulations only needs to carry out 18 calculating cycles,
And the calculating time of each calculating cycle is almost equal with Model Predictive Control.
The two vector switch combined sequences of 10 two small sectors of table
| Sector | On off sequence |
| I | POO-PNN,ONN-PNN,OOO-POO,OOO-ONN,POO-PNO,ONN-PNO |
| II | POO-PNN,ONN-PNN,OOO-POO,OOO-ONN,POO-PON,ONN-PON |
| III | PPO-PPN,OON-PPN,OOO-ONN,OOO-PPO,OON-PON,PPO-PON |
| IV | PPO-PPN,OON-PPN,OOO-ONN,OOO-PPO,OON-OPN,PPO-OPN |
| V | OPO-NPN,NON-NPN,OOO-OPO,OOO-NON,OPO-OPN,NON-OPN |
| VI | OPO-NPN,NON-NPN,OOO-OPO,OOO-NON,OPO-NPO,NON-NPO |
| VII | OPP-NPP,NOO-NPP,OOO-OPP,OOO-NOO,OPP-NPO,NOO-NPO |
| VIII | OPP-NPP,NOO-NPP,OOO-OPP,OOO-NOO,OPP-NOP,NOO-NOP |
| IX | OOP-NNP,NNO-NNP,OOO-OOP,OOO-NNO,OOP-NOP,NNO-NOP |
| X | OOP-NNP,NNO-NNP,OOO-OOP,OOO-NNO,OOP-ONP,NNO-ONP |
| XI | POP-PNP,ONO-PNP,OOO-POP,OOO-ONO,POP-ONP,ONO-ONP |
| XII | POP-PNP,ONO-PNP,OOO-POP,OOO-ONO,POP-PNO,ONO-PNO |
Given active power and reactive power are respectively Pref, QrefIf working as perfect switch stateAct on tri-level inversion
When device, output voltage vector isAnd inverter output power is equal to P when+1 sampling period of kth startsref,
Qref, the variable quantity of active power and reactive power within+1 sampling period of kth is respectively as follows:
By formula (10), formula (6) and formula (7) substitution formula (9) are available:
In formula, χi=ti/Ts, χj=tj/Ts, and 0≤χi≤ 1, χi+χj=1.
In Fig. 4, output vector uiWith ujBetween line be lij, due to ur=uiχi+ujχjAnd χi+χj=1, so working as ui
With ujWhen change in duty cycle, urIn uiWith ujThe straight line l constitutedijUpper variation.With urBetween line be l',With urDistance
It is minimized as dij.WhenWhen among two vectors, in lijD is minimized when vertical with l'i。
In Fig. 5, if givenThe case where when not among two vectors.At this point, in urWith uiOr ujIt is taken when equal
Minimum value dij.The cost function of formula (11) obtains minimum value as a result, are as follows:
Therefore, to export optimal two vector switch sequence, can first to small sector locating for desired output voltage vector into
Small sector where optimal two vector switch sequence can be obtained in row judgement.
In Fig. 6,In I sector IaWith Section II sector IbWhen the big sector of synthesis, cIaIt is the small sector I of IaIn
The heart, cIbIt is the small sector I of Section IIbCenter, dIaAnd dIbIt is respectivelyTo cIaWith arrive cIbDistance.SoLocating small sector can
To pass throughIt is obtained to the distance of this small sector centers.In Fig. 6, whenIn IbWhen sector,To IbCenter cIbDistance
It is less than IaCenter cIaDistance.To the calculation formula of vector centre distance are as follows:
Wherein, small sector output center voltage vector are as follows:
In formula, (uα0,uβ0) it is the zero vector for constituting sector, (uαm,uβm) it is middle vector, (uαl,uβl) it is long vector.
The active power of the corresponding output center vector of formula (14) and the change rate of reactive power are as follows:
So selecting the cost function J ' of small sector when not considering capacitor neutral point voltage balance are as follows:
J '=[Pref-P(k)-fpcTs]2+[Qref-Q(k)-fqcTs]2 (16)
Behind small sector where finding out desired output voltage vector, need to account for the optimal of two vectorial combinations each in small sector
Empty ratio is calculated, and the action time of two of them vector is respectively tiAnd tj, tiIt can be by enabling cost function J to tiDerivation
It obtains:
Enable dJ/dti=0 obtains calculating tiFormula are as follows:
Guarantee 0≤t simultaneouslyi≤Ts.In addition, by Ts=ti+tjObtain tj=Ts-ti。
In the cost function for selecting optimal two vector switch sequence, neutral point voltage balance, two capacitor C are considered1, C2's
Voltage difference are as follows:
Wherein, uo=uc2-uc1For the voltage difference of bus capacitor, C is the size of two capacitors of DC side, viabcFor inverter
Switch state, tiIt is the corresponding effect duration of switch state, | viabc|={ | via|,|vib|,|vic|}T,vix(x=a, b, c)
∈ { -1,0,1 }, iabcIt is the line current and i of connected systemabc={ ia,ib,ic}。
Consider capacitor neutral point voltage balance, find out in small sector the optimal two vector switch sequence in a switch periods,
Define cost function J " are as follows:
J "=[Pref-P(k)-fpiti-fpjtj]2+[Qref-Q(k)-fqiti-fqjtj]2+λ|uo(k+1)| (20)
Wherein the value of λ is 0.1, and finding out from above-mentioned calculated result makes cost function be minimized corresponding two arrows
Amount, according to the corresponding duty ratio of two vector switch sequences, synthesis makes the smallest optimal vector of cost function.
By analysis above, the first step of the model prediction power control based on two Vector modulations is first carried out below, is taken
The center vector of small sector calculates the active-power P of+1 start time in sampling period of kthi(k+1) and reactive power Qi(k+
1) it, then brings first cost function J ' into and acquires small sector where optimal two vector switch sequence.For seeking optimal two vector
The formula of small sector is as follows where on off sequence:
After finding out the sector where optimal two vector switch sequence, second step is carried out, by the on off sequence in corresponding sector
It brings into second cost function J ", the corresponding on off sequence of cost function minimum value is optimized switching sequence.For asking most
The formula of excellent two vector switch sequence is as follows:
Optimal two vector switch of three-level inverter is acquired using the model prediction power control based on two Vector modulations
Sequence and its action time, and then three-level inverter switching device is controlled.When reality output, due to switch state N
It is extremely complex to the switching between P, in order to avoid being not in the switching between N and P when the switching of adjacent sectors switch state, adopt
Two vector switch sequences are exported with the implementation method that small vector is concentrated.Small vector is placed among on off sequence, by zero vector/
Middle vector/big vector action time equal part is on both sides.This control strategy realizes constant switching frequency control, active balance
The mid-point voltage of two capacitors reduces the harmonic content of output electric current, relative to prediction optimized switching sequence Direct Power control
System and modulation pattern PREDICTIVE CONTROL, reduce a large amount of operand, have saved the computing resource of control chip.
In Fig. 7, the three-level inverter model prediction power control system flow chart of two Vector modulations is given.Program
It is summarized as follows: firstly, finding out the center vector of 12 small sectors and by its substitution formula (15), finding out corresponding active power and nothing
Function power conversion rate, then substitute into first cost function J ', obtain the center vector for enabling cost function J ' reach minimum value and it
The sector at place；Then, 6 two vector switch sequence v in sector obtained in the first step are calculatedi(i=1~6) and most
Excellent duty ratio, then second cost function J " is substituted into, obtain the optimal two vector switch sequence for enabling cost function J " reach minimum value
The switching device that obtained optimized switching sequence and its duty ratio corresponding are used to control inverter is finally worked, there is it by column
Function power and reactive power track reference power, and DC side mid-point voltage can be balanced.
Wherein, uj1And uj2For the output vector of on off sequence in small sector, tj1And tj2It is their corresponding duty ratios,
Remaining mark meaning is identical with formula.
Three-level inverter model prediction function based on two Vector modulations is constructed using simulation software MATLAB/Simulink
Rate control system carries out simulation study, and wherein simulation system parameters are as shown in table 2.
2 system parameter of table
| Parameter | Value |
| Filter inductance L | 6mH |
| DC bus capacitor C | 4700uF |
| DC voltage | 380V |
| Power grid phase voltage | 127V |
| Mains frequency | 50Hz |
| Sample frequency | 10kHz |
| Switching frequency | 10kHz |
| Dead time | 3us |
| With reference to active power | 3.5kW |
| With reference to reactive power | 0kVar |
By emulation, the model prediction power control based on two Vector modulations is provided to three-level three-phase gird-connected inverter
Control performance.In emulation, at the time of 10ms, by three level grid-connected inverters it is given with reference to active power from 0 promoted to
3.5kW。
In fig. 8, inverter output line in the model prediction power control system emulation based on two Vector modulations is given
The dynamic response of voltage；In Fig. 9, grid line in the model prediction power control system emulation based on two Vector modulations is given
The dynamic response of electric current；In Figure 10, power grid in the model prediction power control system emulation based on two Vector modulations is given
Active and idle dynamic response；In Figure 11, the model prediction power control system emulation based on two Vector modulations is given
DC capacitor voltage dynamic response.It can be seen that the model prediction based on two Vector modulations from simulation result above
Power control system not only reduces switching number and calculating cycle, is effectively saved computing resource, and can compare
Given active power and reactive power are tracked well, reduces the ripple in alternating current, balance mid-point voltage.
The above embodiment is a preferred embodiment of the present invention, but embodiments of the present invention are not by above-described embodiment
Limitation, other any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present invention,
It should be equivalent substitute mode, be included within the scope of the present invention.
Claims (3)
1. the three-level inverter model prediction Poewr control method based on two Vector modulations characterized by comprising be directed to three
27 all switch states are divided into 12 small sectors on the basis of 6 big sectors by level three-phase grid-connected inverter；First
Step includes the small sector where desired output voltage vector with first cost function selection, then passes through second cost function
Optimal two vector switch sequence is selected in the small sector obtained in the first step, finally utilizes two of three-level inverter selection
The corresponding switch state of vector is controlled according to device for power switching of the corresponding duty ratio to inverter；
Under the influence of negligible resistance, find out in three phase network at static two phase coordinate systems α β, active power and reactive power
The differential equation:
Wherein, (eα,eβ) and (iα,iβ) network voltage and electric current under static two phase coordinate systems α β are represented, L is alternating current filter
Inductance, ω indicate that electrical angular speed, P represent active power, and Q represents reactive power, when inverter switching states are viWhen, inversion
The voltage that device is exported at static two phase coordinate systems α β is ui(uαi,uβi), it is input to grid side active power and reactive power
Derivative is expressed as fpi,fqi, so above formula can also be indicated are as follows:
Assuming that active power and reactive power of the three-level inverter when k-th of sampling period starts are respectively P (k), Q (k),
By two voltage vector voltage vector ui,ujT is acted on respectivelyi,tjAfter time, when+1 sampling period of kth starts, inversion
The active power and reactive power predicted value of device output are as follows:
If the sampling time is Ts, since each sampling period, only there are two vectors to act on, so Ts=ti+tj；
Zero vector is taken respectively, and the middle big vector of vector sum forms the center of small sector, distinguishes using this 12 centrally located vectors
Calculate the active-power P (k+1) and reactive power Q (k+1) of+1 start time in sampling period of kth；A cost function is defined,
From the sector found out where making the smallest center vector of cost function in calculated result, at this moment do not consider that capacitor mid-point voltage is flat first
Weighing apparatus defines cost function J ' are as follows:
J '=[Pref-P(k)-fpcTs]2+[Qref-Q(k)-fqcTs]2 (4)
Wherein, PrefIt is given active power value, QrefIt is given reactive power value, and fpc,fqcIt is output center vector pair
The change rate of the active power and reactive power answered, finding out from above-mentioned calculated result makes the smallest center vector of cost function J '
The sector at place, then sector where two vectors needed for the sector is；
In seeking small sector before optimal two vector switch sequence, first the optimal of two vectorial combinations each in small sector is accounted for
Empty ratio is calculated, and the action time of two of them vector is respectively tiAnd tj, tiIt can be by enabling cost function J to tiDerivation,
And enable it be equal to 0 and obtain, define cost function J are as follows:
J=Δ P2+ΔQ2=[Pref-P(k)-fpiti-fpjtj]2+[Qref-Q(k)-fqiti-fqjtj]2 (5)
It obtains calculating tiFormula are as follows:
In addition, by Ts=ti+tjObtain tj=Ts-ti；
In cost function, neutral point voltage balance, mid-point voltage equation are considered are as follows:
Wherein, uo=uc1-uc2For the voltage difference of bus capacitor, C is the size of two capacitors of DC side, viabcFor opening for inverter
Off status, tiIt is the corresponding effect duration of switch state, | viabc|={ | via|,|vib|,|vic|}T,vix(x=a, b, c) ∈-
1,0,1 }, iabcIt is the line current and i of connected systemabc={ ia,ib,ic}；
Consider capacitor neutral point voltage balance, finds out optimal two vector switch sequence, definition in a switch periods in small sector
Cost function J " are as follows:
J "=[Pref-P(k)-fpiti-fpjtj]2+[Qref-Q(k)-fqiti-fqjtj]2+λ|uo(k+1)| (8)
Finding out from above-mentioned calculated result makes cost function be minimized corresponding two vectors, accounts for according on off sequence is corresponding
Empty ratio, synthesis make the smallest optimal vector of cost function；
Finally, being controlled using two obtained vectors and its corresponding duty ratio three-level inverter.
2. the three-level inverter model prediction Poewr control method according to claim 1 based on two Vector modulations,
It is characterized in that, the value of λ is 0.1 in formula (8).
3. the three-level inverter model prediction Poewr control method according to claim 1 based on two Vector modulations,
It is characterized in that, in order to avoid being not in the switching between N and P when the switching of adjacent sectors switch state, is concentrated using small vector
Implementation method export two vector switch sequences, i.e., small vector is placed among on off sequence, by zero vector/middle vector/big arrow
Action time equal part is measured on both sides.
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